Spectroscopy is the study of the interaction between radiation (electromagnetic radiation, or light, as well as particle radiation) and matter. Spectroscopy is often used in physical and analytical chemistry for the identification of substances through the spectrum emitted from or absorbed by them.
In a Laser Induced Breakdown Spectroscopy (LIBS), a highly energetic laser pulse is used as an excitation source. LIBS can analyze any matter regardless of the state of the matter. Since all elements emit light when excited to sufficiently high temperatures, LIBS can detect all elements, limited only by the power of the laser as well as the sensitivity and wavelength range of the spectrograph and/or detector.
Recently, LIBS has been used to help identify hazardous compounds. Detection of hazardous substances typically requires a laser source that is tunable in the spectral region containing absorption features of the compounds of interest. For many nitrogen containing compounds such as explosives and other hazardous gases this is in the long wave infrared (LWIR) spectral region from 7-14 μm.
Generation of long wavelength laser light is complicated because relatively few direct laser sources exist in this spectral region. Most efficient long wave infrared laser sources (e.g., carbon dioxide [CO2] gas lasers) have limited tuning range, resulting in limited ability to access the spectral signatures of materials of interest in spectroscopic detection. Those efficient techniques that possess broad tunability tend to produce broad spectral linewidth (or line width) as well.
Nonlinear optical frequency conversion techniques are another option to convert light from shorter wavelengths into the desired longer wavelengths. While various nonlinear optical techniques have been devised that permit the generation of tunable laser light in the LWIR spectral region, most suffer from low efficiency, that is low power delivered in the desired spectral region from a given amount of power from the initial optical or electrical source.
These nonlinear optical frequency conversion techniques are typically inefficient for two reasons. First, due to quantum efficiency, photons at the shorter wavelength are converted into those at the longer wavelength resulting in a power decrease equal to the ratio of the wavelengths. Second, due to photon conversion efficiency, only a fraction of the available photons at the shorter wavelength will be converted to photons at the longer wavelength. The optical conversion efficiency is the product of the quantum and photon conversion efficiencies and, with starting wavelengths in the 1 μm region of commonly available solid state lasers, is typically well under 10% for conversion into the long wave infrared region.
Therefore, it would be desirable to provide an apparatus and method that overcomes the above problems.